Low Density Press-Hardening Steel Having Enhanced Mechanical Properties

ABSTRACT

A method of forming a shaped steel object is provided. The method includes cutting a blank from an alloy composition including 0.05-0.5 wt. % carbon, 4-12 wt. % manganese, 1-8 wt. % aluminum, 0-0.4 wt. % vanadium, and a remainder balance of iron. The method also includes heating the blank until the blank is austenitized to form a heated blank, transferring the heated blank to a press, forming the heating blank into a predetermined shape to form a stamped object, and decreasing the temperature of the stamped object to a temperature between a martensite start (Ms) temperature of the alloy composition and a martensite final (Mf) temperature of the alloy composition to form a shaped steel object comprising martensite and retained austenite.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 17/251,655filed on Dec. 11, 2020, which is a U.S. National Phase Application under35 U.S.C. 371 of International Application No. PCT/CN2018/091751 filedon Jun. 19, 2018. The entire disclosures of the above applications areincorporated herein by reference.

INTRODUCTION

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Press-hardening steel (PHS), also referred to as “hot-stamped steel” or“hot-formed steel” is used in various industries and applications,including general manufacturing, construction equipment, automotive orother transportation industries, home or industrial structures, and thelike. It is one of the strongest steels used for automotive bodystructural applications, having tensile strength properties on the orderof about 1,500 mega-Pascal (MPa). Such steel has desirable properties,including forming steel components having high strength-to-weightratios. For example, when manufacturing vehicles, especiallyautomobiles, continual improvement in fuel efficiency and performance isdesirable. PHS components are often used for forming load-bearingcomponents, like door beams, which usually require high strengthmaterials. Thus, the finished state of these steels are designed to havehigh strength and enough ductility to resist external forces such as,for example, resisting intrusion into the passenger compartment withoutfracturing so as to provide protection to the occupants. Moreover,galvanized PHS components may provide cathodic protection.

Many PHS processes involve austenitization in a furnace of a sheet steelblank, immediately followed by pressing and quenching of the sheet indies. Austenitization is typically conducted in the range of about 880°C. to 950° C. There are two main types of PHS processes: indirect anddirect. In the direct method, the PHS component is formed and pressedsimultaneously between dies, which quenches the steel. In the indirectmethod, the PHS component is cold formed to an intermediate partialshape before austenitization and the subsequent pressing and quenchingsteps. The quenching of the PHS component hardens the component bytransforming the microstructure from austenite to martensite. An oxidelayer often forms during the transfer from the furnace to the dies whenthe PHS is not pre-coated or pre-treated with an anti-oxidationmaterial. Therefore, after quenching, the oxide must be removed from thePHS component and the dies. The oxide is typically removed, i.e.,descaled, by shot blasting.

The PHS component may be coated prior to applicable pre-cold forming (ifthe indirect process is used) or austenitization. Coating the PHScomponent provides a protective layer (e.g., galvanic protection oranti-oxidation protection) to the underlying steel component. Suchcoatings typically include an aluminum-silicon alloy for anti-oxidationprotection and/or zinc for cathodic protection. Zinc coatings, forexample, act as sacrificial layers and corrode instead of the steelcomponent, even where the steel is exposed. Zinc coatings also generateoxides on PHS components' surfaces, which are removed by shot blasting.Accordingly, alloy compositions that do not require coatings and thatprovide improved strength and ductility are desired.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In various aspects, the current technology provides a method of forminga shaped steel object. The method includes cutting a blank from an alloycomposition. The alloy composition includes carbon (C) at aconcentration of greater than or equal to about 0.05 wt. % to less thanor equal to about 0.5 wt. % of the alloy composition, manganese (Mn) ata concentration of greater than or equal to about 4 wt. % to less thanor equal to about 12 wt. % of the alloy composition, aluminum (Al) at aconcentration of greater than or equal to about 1 wt. % to less than orequal to about 8 wt. % of the alloy composition, vanadium (V) at aconcentration of greater than 0 wt. % to less than or equal to about 0.4wt. % of the alloy composition, and a balance of the alloy compositionbeing iron (Fe). The method also includes heating the blank until theblank is austenitized, transferring the heated blank to a press, formingthe heated blank into a predetermined shape defined by the press togenerate a stamped object, and decreasing the temperature of the stampedobject to a temperature between a martensite start (Ms) temperature ofthe alloy composition and a martensite final (Mf) temperature of thealloy composition to form a shaped steel object including martensite andretained austenite.

In one aspect, the alloy composition further includes zirconium (Zr) ata concentration of greater than 0 wt. % to less than or equal to about0.5 wt. % of the alloy composition.

In one aspect, the alloy composition further includes at least one ofnickel (Ni) at a concentration of greater than 0 wt. % to less than orequal to about 5 wt. % of the alloy composition, molybdenum (Mo) at aconcentration of greater than 0 wt. % to less than or equal to about 0.5wt. % of the alloy composition, niobium (Nb) at a concentration ofgreater than 0 wt. % to less than or equal to about 0.2 wt. % of thealloy composition, copper (Cu) at a concentration of greater than 0 wt.% to less than or equal to about 3 wt. % of the alloy composition,titanium (Ti) at a concentration of greater than 0 wt. % to less than orequal to about 0.1 wt. % of the alloy composition, nitrogen (N) at aconcentration of greater than 0 wt. % to less than or equal to about0.01 wt. % of the alloy composition, and boron (B) at a concentration ofgreater than 0 wt. % to less than or equal to about 0.005 wt. % of thealloy composition.

In one aspect, the Mn is at a concentration of greater than or equal toabout 6 wt. % to less than or equal to about 10 wt. % and the Al is at aconcentration of greater than or equal to about 2 wt. % to less than orequal to about 5 wt. %.

In one aspect, the C is at a concentration of greater than or equal toabout 0.1 wt. % to less than or equal to about 0.45 wt. %.

In one aspect, the alloy composition is in the form of a coil.

In one aspect, the heating the blank includes heating the blank to atemperature of greater than or equal to about 900° C. to less than orequal to about 950° C. for a time period of greater than or equal toabout 1 minute to less than or equal to about 60 minutes.

In one aspect, the temperature between the Ms temperature of the alloycomposition and the Mf temperature of the alloy composition is ambienttemperature.

In one aspect, the decreasing the temperature includes decreasing thetemperature at a rate of greater than or equal to about 5° Cs⁻¹ to lessthan or equal to about 300° Cs⁻¹.

In one aspect, the method further includes, prior to the heating theblank until the blank is austenitized, preoxidizing the alloycomposition by heating the alloy composition to a temperature of greaterthan or equal to about 500° C. to less than or equal to about 600° C.for a time period of greater than or equal to about 1 minute to lessthan or equal to about 60 minutes.

In one aspect, the method further includes, after the decreasing thetemperature, tempering the shaped steel object.

In one aspect, the tempering the shaped steel object includes heatingthe shaped steel object to a temperature greater than or equal to about150° C. to less than or equal to about 300° C. for a time period ofgreater than or equal to about 1 minute to less than or equal to about120 minutes, and cooling the shaped steel object to ambient temperature.

In one aspect, the shaped steel object has a higher strength and a lowerweight relative to an equivalent shaped steel object formed from 22MnB5.

In various embodiments, the current technology also provides a method offorming a shaped steel object. The method includes heating a blank to atemperature of greater than or equal to about 900° C. to less than orequal to about 950° C. for a time period of greater than or equal toabout 1 minute to less than or equal to about 60 minutes to generate aheated blank. The blank is composed of an alloy composition includingcarbon (C) at a concentration of greater than or equal to about 0.05 wt.% to less than or equal to about 0.5 wt. % of the alloy composition,manganese (Mn) at a concentration of greater than or equal to about 4wt. % to less than or equal to about 12 wt. % of the alloy composition,aluminum (Al) at a concentration of greater than or equal to about 1 wt.% to less than or equal to about 8 wt. % of the alloy composition,vanadium (V) at a concentration of greater than 0 wt. % to less than orequal to about 0.4 wt. % of the alloy composition, zirconium (Zr) at aconcentration of greater than 0 wt. % to less than or equal to about 0.5wt. % of the alloy composition, and a balance of the alloy compositionbeing iron (Fe). The method also includes forming the heated blank intoa predetermined shape in a press to generate a stamped object, quenchingthe stamped object by decreasing the temperature of the stamped objectto about ambient temperature to form a shaped steel object includingmartensite and retained austenite, and tempering the shaped steel objectby heating the shaped steel object to greater than or equal to about150° C. to less than or equal to about 300° C. for a time period ofgreater than or equal to about 1 minute to less than or equal to about120 minutes and then decreasing the temperature of the shaped steelobject to ambient temperature.

In one aspect, the shaped steel object is an automobile part selectedfrom the group consisting of a pillar, a bumper, a roof rail, a rockerrail, a tunnel, a beam, and a reinforcement.

In various embodiments, the current technology yet further provides analloy composition. The alloy composition includes carbon (C) at aconcentration of greater than or equal to about 0.05 wt. % to less thanor equal to about 0.5 wt. % of the alloy composition, manganese (Mn) ata concentration of greater than or equal to about 4 wt. % to less thanor equal to about 12 wt. % of the alloy composition, aluminum (Al) at aconcentration of greater than or equal to about 1 wt. % to less than orequal to about 8 wt. % of the alloy composition, vanadium (V) at aconcentration of greater than 0 wt. % to less than or equal to about 0.4wt. % of the alloy composition, zirconium (Zr) at a concentration ofgreater than 0 wt. % to less than or equal to about 0.5 wt. % of thealloy composition, and a balance of the alloy composition being iron(Fe).

In one aspect, the alloy composition has a higher strength and lowerweight after press hardening relative to an equivalent 22MnB5 steelafter press hardening.

In one aspect, after press hardening, the alloy composition includesgreater than or equal to about 80 wt. % to less than or equal to about95 wt. % martensite and greater than or equal to about 5 wt. % to lessthan or equal to about 20 wt. % retained austenite.

In one aspect, after press hardening, the alloy composition has amartensite:retained austenite ratio that increases when a load isapplied to the alloy composition.

In one aspect, the current technology provides an automobile partincluding the alloy composition. The automobile part is a pillar, abumper, a roof rail, a rocker rail, a tunnel, a beam, or areinforcement.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a graph showing a temperature profile used in a method of hotstamping 22MnB5 steel.

FIG. 2 is a flow chart showing aspects of a method for making a shapedsteel object according to various aspects of the current technology.

FIG. 3 is a graph showing a temperature profile used in a method ofmaking a shaped steel object according to various aspects of the currenttechnology.

FIG. 4 shows an electron backscatter diffraction (EBSD) image ofmicrostructures of a hot stamped alloy composition made according tovarious aspects of the current technology.

FIG. 5 is a graphic illustration that demonstratestransformation-induced plasticity.

FIG. 6 is a graph of stress versus strain for hot stamped 22MnB5 and ahot stamped alloy composition according to various aspects of thecurrent technology.

FIG. 7 is a graph of stress versus strain for hot stamped 22MnB5 and ahot stamped alloy composition according to various aspects of thecurrent technology.

FIG. 8 is a graphic illustration demonstrating lattice dilationresulting from the addition of aluminum into an iron lattice.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific compositions, components, devices, and methods, to provide athorough understanding of embodiments of the present disclosure. It willbe apparent to those skilled in the art that specific details need notbe employed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, elements, compositions, steps, integers, operations, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. Although the open-ended term “comprising,” is tobe understood as a non-restrictive term used to describe and claimvarious embodiments set forth herein, in certain aspects, the term mayalternatively be understood to instead be a more limiting andrestrictive term, such as “consisting of” or “consisting essentiallyof.” Thus, for any given embodiment reciting compositions, materials,components, elements, features, integers, operations, and/or processsteps, the present disclosure also specifically includes embodimentsconsisting of, or consisting essentially of, such recited compositions,materials, components, elements, features, integers, operations, and/orprocess steps. In the case of “consisting of,” the alternativeembodiment excludes any additional compositions, materials, components,elements, features, integers, operations, and/or process steps, while inthe case of “consisting essentially of,” any additional compositions,materials, components, elements, features, integers, operations, and/orprocess steps that materially affect the basic and novel characteristicsare excluded from such an embodiment, but any compositions, materials,components, elements, features, integers, operations, and/or processsteps that do not materially affect the basic and novel characteristicscan be included in the embodiment.

Any method steps, processes, and operations described herein are not tobe construed as necessarily requiring their performance in theparticular order discussed or illustrated, unless specificallyidentified as an order of performance It is also to be understood thatadditional or alternative steps may be employed, unless otherwiseindicated.

When a component, element, or layer is referred to as being “on,”“engaged to,” “connected to,” or “coupled to” another element or layer,it may be directly on, engaged, connected or coupled to the othercomponent, element, or layer, or intervening elements or layers may bepresent. In contrast, when an element is referred to as being “directlyon,” “directly engaged to,” “directly connected to,” or “directlycoupled to” another element or layer, there may be no interveningelements or layers present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.). As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various steps, elements, components, regions, layers and/orsections, these steps, elements, components, regions, layers and/orsections should not be limited by these terms, unless otherwiseindicated. These terms may be only used to distinguish one step,element, component, region, layer or section from another step, element,component, region, layer or section. Terms such as “first,” “second,”and other numerical terms when used herein do not imply a sequence ororder unless clearly indicated by the context. Thus, a first step,element, component, region, layer or section discussed below could betermed a second step, element, component, region, layer or sectionwithout departing from the teachings of the example embodiments.

Spatially or temporally relative terms, such as “before,” “after,”“inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and thelike, may be used herein for ease of description to describe one elementor feature's relationship to another element(s) or feature(s) asillustrated in the figures. Spatially or temporally relative terms maybe intended to encompass different orientations of the device or systemin use or operation in addition to the orientation depicted in thefigures.

Throughout this disclosure, the numerical values represent approximatemeasures or limits to ranges to encompass minor deviations from thegiven values and embodiments having about the value mentioned as well asthose having exactly the value mentioned. Other than in the workingexamples provided at the end of the detailed description, all numericalvalues of parameters (e.g., of quantities or conditions) in thisspecification, including the appended claims, are to be understood asbeing modified in all instances by the term “about” whether or not“about” actually appears before the numerical value. “About” indicatesthat the stated numerical value allows some slight imprecision (withsome approach to exactness in the value; approximately or reasonablyclose to the value; nearly). If the imprecision provided by “about” isnot otherwise understood in the art with this ordinary meaning, then“about” as used herein indicates at least variations that may arise fromordinary methods of measuring and using such parameters. For example,“about” may comprise a variation of less than or equal to 5%, optionallyless than or equal to 4%, optionally less than or equal to 3%,optionally less than or equal to 2%, optionally less than or equal to1%, optionally less than or equal to 0.5%, and in certain aspects,optionally less than or equal to 0.1%.

In addition, disclosure of ranges includes disclosure of all values andfurther divided ranges within the entire range, including endpoints andsub-ranges given for the ranges.

Example embodiments will now be described more fully with reference tothe accompanying drawings.

22MnB5 is a press-hardening steel (PHS) that is used for manufacturingvarious automobile parts. 22MnB5 comprises about 0.22 wt. % carbon (C),about 1.2 wt. % manganese (Mn), about 0.05 wt. % aluminum (Al), about0.033 wt. % titanium (Ti), about 0.003 wt. % boron (B), and about 0.006wt. % nitrogen (N). 22MnB5 steel can be hot stamped as a bare uncoatedalloy. When uncoated, hot stamped 22MnB5 undergoes oxidation, which mustbe removed in a subsequent cleaning or descaling process. Therefore,22MnB5 is often coated with aluminum-silicon (Al—Si) or zinc (Zn) tominimize oxidation and to preclude a subsequent cleaning process. FIG. 1shows a temperature profile 10 for hot stamping 22MnB5. The temperatureprofile 10 has a y-axis 12 representing temperature and an x-axis 14representing time. As shown in the temperature profile 10, 22MnB5 isheated to an austenitization temperature 16 where the 22MnB5 becomesfully austenitized. The 22MnB5 is then formed into a shape at a formingtemperature 18 and a decreasing temperature 20 quenches the 22MnB5,until the 22MnB5 reaches ambient temperature 22. Because 22MnB5 has amartensite start (Ms) temperature 24 of about 425° C. and a martensitefinal (Mf) temperature 26 of about 280° C., when the 22MnB5 reachesambient temperature 22, the 22MnB5 has a microstructure that is about100% martensite. The resulting hot pressed steel has an ultimate tensilestrength (UTS) of less than about 1500 MPa and a density of about 7.8g/cm³.

The current technology provides an alloy composition that, after hotpressing, has a higher UTS and a lower density relative to hot pressed22MnB5. The alloy composition can be used to manufacture any object thatis generally made by hot stamping, such as, for example, a vehicle part.Non-limiting examples of vehicles that have parts suitable to beproduced by the current method include bicycles, automobiles,motorcycles, boats, tractors, buses, mobile homes, campers, gliders,airplanes, and military vehicles, such as tanks. For example, the alloycomposition can be used for automobile parts, such as pillars (e.g.,A-pillars and B-pillars), bumpers (e.g., front bumpers and rearbumpers), roof rails, rocker rails, tunnels, beams (e.g., side impactbeams), or reinforcements (e.g., door reinforcements).

The alloy composition of the current technology comprises carbon (C) andmanganese (Mn) at concentrations that are generally higher than theircorresponding concentrations in 22MnB5 steel. These C and Mnconcentrations provide a hot stamped steel comprising martensite andretained austenite, which lead to improved UTS and ductility. Moreparticularly, the alloy composition comprises carbon (C) at aconcentration of greater than or equal to about 0.05 wt. % to less thanor equal to about 0.5 wt. %, or greater than or equal to about 0.1 wt. %to less than or equal to about 0.45 wt. %, and manganese (Mn) at aconcentration of greater than or equal to about 4 wt. % to less than orequal to about 12 wt. %, greater than or equal to about 5 wt. % to lessthan or equal to about 11 wt. %, or greater than or equal to about 6 wt.% to less than or equal to about 10 wt. %.

The alloy composition of the current technology also comprises aluminum(Al) at a concentration that is higher than the Al concentration in22MnB5 steel. This increased Al concentration decreases the density ofthe resulting hot pressed steel and provides resistance to oxidation. Inparticular, the alloy composition comprises aluminum (Al) at aconcentration of greater than or equal to about 1 wt. % to less than orequal to about 8 wt. %, or greater than or equal to about 2 wt. % toless than or equal to about 6 wt. %.

The alloy composition of the current technology also comprises vanadium(V), which is generally not present in 22MnB5 steel. The vanadium (V)refines the grain size of resulting hot pressed steel and inhibits orminimizes crack propagation, which improves ductility of the resultinghot pressed steel relative to 22MnB5 steel. In particular, the alloycomposition comprises vanadium (V) at a concentration of greater than 0wt. % to less than or equal to about 0.4 wt. %, or greater than or equalto about 0.01 wt. % to less than or equal to about 0.4 wt. %.

Under some conditions, the alloy composition is a solid solutioncomprising Al and nitrogen (N), which react and generate aluminumnitride (AlN) inclusion particles, which have a size of about 2-10 μmand decrease toughness. Relative to Al, zirconium (Zr) has a highersolubility in the solid solution. Zr reacts with N to form zirconiumnitride (ZrN), which has a nanometer grain size and minimal effect ontoughness. Therefore, by including Zr, ZrN may form, which minimizes theamount of AlN formed and mitigates the negative effect that AlN has onsteel toughness. Accordingly, the alloy composition of the currenttechnology also comprises zirconium (Zr) at a concentration of greaterthan 0 wt. % to less than or equal to about 0.5 wt. %, or greater thanor equal to about 0.005 wt. % to less than or equal to about 0.2 wt. %.

A balance of the alloy composition is iron (Fe).

In various embodiments, the alloy composition further comprises titanium(Ti) at a concentration of greater than 0 wt. % to less than or equal toabout 0.05 wt. %, or greater than or equal to about 0.001 wt. % to lessthan or equal to about 0.033 wt. %.

In various embodiments, the alloy composition further comprises boron(B) at a concentration of greater than 0 wt. % to less than or equal toabout 0.005 wt. %, or greater than 0 wt. % to less than or equal toabout 0.003 wt. %.

In various embodiments, the alloy composition further comprises nitrogen(N) at a concentration of greater than 0 wt. % to less than or equal toabout 0.01 wt. %.

In various embodiments, the alloy composition further comprisesmolybdenum (Mo) at a concentration of greater than 0 wt. % to less thanor equal to about 0.5 wt. %.

In various embodiments, the alloy composition further comprises niobium(Nb) at a concentration of greater than 0 wt. % to less than or equal toabout 0.2 wt. %.

In various embodiments, the alloy composition further comprises nickel(Ni) at a concentration of greater than 0 wt. % to less than or equal toabout 5 wt. %, greater than or equal to about 0.01 wt. % to less than orequal to about 3 wt. %, or less than or equal to about 3 wt. %.

In various embodiments, the alloy composition further comprises copper(Cu) at a concentration of greater than 0 wt. % to less than or equal toabout 3 wt. %.

The alloy composition can include various combinations of C, Mn, Al, V,Zr, Ti, B, N, Mo, Nb, Ni, Cu, and Fe at their respective concentrationsdescribed above. In some embodiments, the alloy composition consistsessentially of C, Mn, Al, V, Zr, Ti, B, N, Mo, Nb, Ni, Cu, and Fe. Asdescribed above, the term “consists essentially of” means the alloycomposition precludes additional compositions, materials, components,elements, and/or features that materially affect the basic and novelcharacteristics of the alloy composition, such as strength andductility, but any compositions, materials, components, elements, and/orfeatures that do not materially affect the basic and novelcharacteristics, such as impurities, can be included.

In one embodiment, the alloy composition consists essentially of greaterthan or equal to about 0.05 wt. % to less than or equal to about 0.5 wt.% C, greater than or equal to about 4 wt. % to less than or equal toabout 12 wt. % Mn, greater than or equal to about 1 wt. % to less thanor equal to about 8 wt. % Al, greater than 0 wt. % to less than or equalto about 0.4 wt. % V, greater than 0 wt. % to less than or equal toabout 0.5 wt. % Zr, greater than 0 wt. % to less than or equal to about0.1 wt. % Ti, greater than 0 wt. % to less than or equal to about 0.005wt. % B, greater than 0 wt. % to less than or equal to about 0.01 wt. %N, greater than 0 wt. % to less than or equal to about 0.5 wt. % Mo,greater than 0 wt. % to less than or equal to about 0.2 wt. % Nb,greater than 0 wt. % to less than or equal to about 5 wt. % Ni, greaterthan 0 wt. % to less than or equal to about 3 wt. % Cu, and a remainingbalance of Fe. In another embodiment, the alloy composition consists ofgreater than or equal to about 0.05 wt. % to less than or equal to about0.5 wt. % C, greater than or equal to about 4 wt. % to less than orequal to about 12 wt. % Mn, greater than or equal to about 1 wt. % toless than or equal to about 8 wt. % Al, greater than 0 wt. % to lessthan or equal to about 0.4 wt. % V, greater than 0 wt. % to less than orequal to about 0.5 wt. % Zr, greater than 0 wt. % to less than or equalto about 0.1 wt. % Ti, greater than 0 wt. % to less than or equal toabout 0.005 wt. % B, greater than 0 wt. % to less than or equal to about0.01 wt. % N, greater than 0 wt. % to less than or equal to about 0.5wt. % Mo, greater than 0 wt. % to less than or equal to about 0.2 wt. %Nb, greater than 0 wt. % to less than or equal to about 5 wt. % Ni,greater than 0 wt. % to less than or equal to about 3 wt. % Cu, and aremaining balance of Fe.

In one embodiment, the alloy composition consists essentially of greaterthan or equal to about 0.05 wt. % to less than or equal to about 0.5 wt.% C, greater than or equal to about 4 wt. % to less than or equal toabout 12 wt. % Mn, greater than or equal to about 1 wt. % to less thanor equal to about 8 wt. % Al, greater than 0 wt. % to less than or equalto about 0.4 wt. % V, greater than 0 wt. % to less than or equal toabout 0.5 wt. % Zr, and a remainder balance of Fe. In anotherembodiment, the alloy composition consists of greater than or equal toabout 0.05 wt. % to less than or equal to about 0.5 wt. % C, greaterthan or equal to about 4 wt. % to less than or equal to about 12 wt. %Mn, greater than or equal to about 1 wt. % to less than or equal toabout 8 wt. % Al, greater than 0 wt. % to less than or equal to about0.4 wt. % V, greater than 0 wt. % to less than or equal to about 0.5 wt.% Zr, and a remainder balance of Fe.

In one embodiment, the alloy composition consists essentially of greaterthan or equal to about 0.05 wt. % to less than or equal to about 0.5 wt.% C, greater than or equal to about 4 wt. % to less than or equal toabout 12 wt. % Mn, greater than or equal to about 1 wt. % to less thanor equal to about 8 wt. % Al, greater than 0 wt. % to less than or equalto about 0.4 wt. % V, greater than 0 wt. % to less than or equal toabout 0.5 wt. % Zr, greater than 0 wt. % to less than or equal to about0.1 wt. % Ti, greater than 0 wt. % to less than or equal to about 0.005wt. % B, greater than 0 wt. % to less than or equal to about 0.01 wt. %N, and a remainder balance of Fe. In another embodiment, the alloycomposition consists of greater than or equal to about 0.05 wt. % toless than or equal to about 0.5 wt. % C, greater than or equal to about4 wt. % to less than or equal to about 12 wt. % Mn, greater than orequal to about 1 wt. % to less than or equal to about 8 wt. % Al,greater than 0 wt. % to less than or equal to about 0.4 wt. % V, greaterthan 0 wt. % to less than or equal to about 0.5 wt. % Zr, greater than 0wt. % to less than or equal to about 0.1 wt. % Ti, greater than 0 wt. %to less than or equal to about 0.005 wt. % B, greater than 0 wt. % toless than or equal to about 0.01 wt. % N, and a remainder balance of Fe.

In one embodiment, the alloy composition consists essentially of greaterthan or equal to about 0.05 wt. % to less than or equal to about 0.5 wt.% C, greater than or equal to about 4 wt. % to less than or equal toabout 12 wt. % Mn, greater than or equal to about 1 wt. % to less thanor equal to about 8 wt. % Al, greater than 0 wt. % to less than or equalto about 0.4 wt. % V, greater than 0 wt. % to less than or equal toabout 0.5 wt. % Zr, greater than 0 wt. % to less than or equal to about0.5 wt. % Mo, greater than 0 wt. % to less than or equal to about 0.2wt. % Nb, greater than 0 wt. % to less than or equal to about 5 wt. %Ni, greater than 0 wt. % to less than or equal to about 3 wt. % Cu, anda remainder balance of Fe. In another embodiment, the alloy compositionconsists of greater than or equal to about 0.05 wt. % to less than orequal to about 0.5 wt. % C, greater than or equal to about 4 wt. % toless than or equal to about 12 wt. % Mn, greater than or equal to about1 wt. % to less than or equal to about 8 wt. % Al, greater than 0 wt. %to less than or equal to about 0.4 wt. % V, greater than 0 wt. % to lessthan or equal to about 0.5 wt. % Zr, greater than 0 wt. % to less thanor equal to about 0.5 wt. % Mo, greater than 0 wt. % to less than orequal to about 0.2 wt. % Nb, greater than 0 wt. % to less than or equalto about 5 wt. % Ni, greater than 0 wt. % to less than or equal to about3 wt. % Cu, and a remainder balance of Fe.

In one embodiment, the alloy composition consists essentially of greaterthan or equal to about 0.05 wt. % to less than or equal to about 0.5 wt.% C, greater than or equal to about 4 wt. % to less than or equal toabout 12 wt. % Mn, greater than or equal to about 1 wt. % to less thanor equal to about 8 wt. % Al, greater than 0 wt. % to less than or equalto about 0.4 wt. % V, greater than 0 wt. % to less than or equal toabout 0.5 wt. % Zr, greater than 0 wt. % to less than or equal to about0.5 wt. % Mo, greater than 0 wt. % to less than or equal to about 5 wt.% Ni, greater than 0 wt. % to less than or equal to about 3 wt. % Cu,and a remainder balance of Fe. In another embodiment, the alloycomposition consists of greater than or equal to about 0.05 wt. % toless than or equal to about 0.5 wt. % C, greater than or equal to about4 wt. % to less than or equal to about 12 wt. % Mn, greater than orequal to about 1 wt. % to less than or equal to about 8 wt. % Al,greater than 0 wt. % to less than or equal to about 0.4 wt. % V, greaterthan 0 wt. % to less than or equal to about 0.5 wt. % Zr, greater than 0wt. % to less than or equal to about 0.5 wt. % Mo, greater than 0 wt. %to less than or equal to about 5 wt. % Ni, greater than 0 wt. % to lessthan or equal to about 3 wt. % Cu, and a remainder balance of Fe.

In one embodiment, the alloy composition consists essentially of greaterthan or equal to about 0.05 wt. % to less than or equal to about 0.5 wt.% C, greater than or equal to about 4 wt. % to less than or equal toabout 12 wt. % Mn, greater than or equal to about 1 wt. % to less thanor equal to about 8 wt. % Al, greater than 0 wt. % to less than or equalto about 0.4 wt. % V, greater than 0 wt. % to less than or equal toabout 0.5 wt. % Mo, greater than 0 wt. % to less than or equal to about5 wt. % Ni, greater than 0 wt. % to less than or equal to about 3 wt. %Cu, and a remainder balance of Fe. In another embodiment, the alloycomposition consists of greater than or equal to about 0.05 wt. % toless than or equal to about 0.5 wt. % C, greater than or equal to about4 wt. % to less than or equal to about 12 wt. % Mn, greater than orequal to about 1 wt. % to less than or equal to about 8 wt. % Al,greater than 0 wt. % to less than or equal to about 0.4 wt. % V, greaterthan 0 wt. % to less than or equal to about 0.5 wt. % Mo, greater than 0wt. % to less than or equal to about 5 wt. % Ni, greater than 0 wt. % toless than or equal to about 3 wt. % Cu, and a remainder balance of Fe.

In one embodiment, the alloy composition comprises C, Mn, Al, and Fe,and optionally comprises at least one of V, Zr, Ti, B, N, Mo, Nb, Ni,and Cu.

In one embodiment, the alloy composition comprises C, Mn, Al, V and Fe,and optionally comprises at least one of Zr, Ti, B, N, Mo, Nb, Ni, andCu.

In one embodiment, the alloy composition comprises C, Mn, Al, Zr and Fe,and optionally comprises at least one of V, Ti, B, N, Mo, Nb, Ni, andCu.

In one embodiment, the alloy composition comprises C, Mn, Al, V, Zr andFe, and optionally comprises at least one of Ti, B, N, Mo, Nb, Ni, andCu.

The alloy composition is provided as a rolled coil or as a sheet with amicrostructure comprising ferrite and cementite. The alloy compositionis either bare (uncoated) and preoxidized, bare and not preoxidized, orcoated with Al—Si or Zn. For example, the alloy composition can bepreoxidized during manufacturing at a steel mill and provided to a useras a bare, preoxidized coil or sheet. Alternatively, the alloycomposition is not preoxidized during manufacturing and is provided to auser as a bare, non-preoxidized coil or sheet. When the alloycomposition reaches a user in non-preoxidized form, the user optionallypreoxidizes the alloy composition prior to hot stamping. Similarly,non-preoxidized alloy composition can be optionally coated duringmanufacturing.

With reference to FIG. 2 , the current technology provides a method 30of forming a shaped steel object. The shaped steel object can be anyobject that is generally made by hot stamping, as described above. Themethod 30 comprises cutting a blank 32 comprising an alloy composition,which can be provided as a coil or sheet. The alloy composition isoptionally coated with, for example, Al—Si or Zn. The alloy compositionis the alloy composition according to the current technology describedherein. The method then comprises transferring the blank 32 to a furnaceor oven 34, and austenitizing the blank 32 by heating the blank 32 to atemperature above a critical transformation temperature (A_(c3)), atwhich ferrite transforms into austenite, to generate a heated blank.Heating is performed until the blank is austenitized, i.e., until theblank comprises at least about 99% austenite or about 100% austenite. Invarious embodiments, the heating comprises heating the blank 32 to atemperature of greater than or equal to about 880° C. to less than orequal to about 1000° C., or greater than or equal to about 900° C. toless than or equal to about 950° C. The heating is performed for a timeperiod of greater than or equal to about 0.5 minutes to less than orequal to about 60 minutes, or greater than or equal to about 1 minute toless than or equal to about 30 minutes.

Optionally by a robotic arm 36, the method 30 comprises transferring theheated blank to a press 38. Here, the method 30 comprises forming theheated blank into a predetermined shape defined by the press to form astamped object. In various embodiments, the forming comprises stampingthe heated blank to generate a stamped object having the predeterminedshape.

While in the press 38, and optionally simultaneously with the forming,the method 30 also comprises quenching the stamped object to form ashaped steel object 40. The quenching comprises decreasing thetemperature of the stamped object to a temperature between a martensitestart (Ms) temperature of the alloy composition and a martensite final(Mf) temperature of the alloy composition to form the shaped steelobject 40. The decreasing the temperature comprises decreasing thetemperature at a rate of greater than or equal to about 5° Cs⁻¹ to lessthan or equal to about 300° Cs⁻¹. In various embodiments, the Mstemperature of the alloy composition is a temperature above ambienttemperature and the Mf temperature of the alloy composition is atemperature below ambient temperature. As such, in some embodiments, thequenching comprises decreasing the temperature to ambient temperature.In other embodiments, the Ms temperature is below ambient temperature(e.g., when the alloy composition comprises 0.5 wt. % C and 12 wt. % Mn)or the Mf temperature is above ambient temperature (e.g., when the alloycomposition comprises 0.05 wt. % C and 4 wt. % Mn). As used herein,“ambient temperature” is standard ambient temperature 25° C. or atemperature greater than or equal to about 10° C. to less than or equalto about 50° C., greater than or equal to about 15° C. to less than orequal to about 40° C., greater than or equal to about 20° C. to lessthan or equal to about 30° C., greater than or equal to about 22° C. toless than or equal to about 28° C., such as a temperature of about 10°C., about 15° C., about 20° C., about 25° C., about 30° C., about 35°C., about 40° C., about 45° C., or about 50° C. As a result of quenchingto a temperature between Ms and Mf, the shaped steel object 40 comprisesmartensite and retained austenite.

Next, the method 30 comprises performing an optional temperingtreatment. As used herein, “tempering” refers to reheating and cooling ahard pressed steel in order to stabilized retained austenite in the hardpressed steel, which enhances strength and ductility. The temperingtreatment comprises transferring the shaped steel object to second ovenor furnace 42 and heating the shaped steel object for a time period ofgreater than or equal to about 1 minute to less than or equal to about120 minutes, or greater than or equal to about 5 minutes to less than orequal to about 60 minutes. In various embodiments, the heating comprisesheating the shaped steel object 40 to a temperature of greater than orequal to about 150° C. to less than or equal to about 300° C. The method30 also includes cooling the shaped steel object back to a temperaturebetween Ms and Mf, such as to ambient temperature in variousembodiments.

In some embodiments, the alloy composition is bare, but has not beenpreoxidized prior to the austenitizing the blank. In such embodiments,the method 30 optionally further comprises, prior to theaustenitization, preoxidizing the alloy composition by heating the alloycomposition to a temperature of greater than or equal to about 500° C.to less than or equal to about 600° C. for a time period of greater thanor equal to about 1 minute to less than or equal to about 60 minutes inair or in a controlled environment comprising N₂ (gas). In variousembodiments, the method 30 is free of at least one of a preoxidationstep, and a descaling step (e.g., shot blasting).

The method 30 is further described in FIG. 3 , which shows a graph 50having a y-axis 52 representing temperature and an x-axis 54representing time. A line 56 on the graph 50 is a cooling profile for analloy composition. Here, the blank is austenitized, i.e., heated to afinal temperature 58 that is above a critical transformation temperature(A_(c3)) 60 of the alloy composition. The final temperature 58, asdescribed above, is greater than or equal to about 88° C. to less thanor equal to about 1000° C., or greater than or equal to about 900° C. toless than or equal to about 950° C.

The austenitized blank is then stamped or hot formed into a stampedobject in a press at a temperature 62 between the final temperature 58and A_(c3) 60. The stamped object is then quenched, i.e., cooled, at aconstant quench rate of greater than or equal to about 5° Cs⁻¹ to lessthan or equal to about 300° Cs⁻¹, or great than or equal to about 60°Cs⁻¹ to less than or equal to about 100° Cs⁻¹ until the temperaturedecreases below a martensite start (Ms) temperature 64, but above amartensite final (Mf) temperature 66, such as to ambient temperature 68(in some embodiments) to form a shaped steel object.

As discussed above, a result of quenching to a temperature between Msand Mf, the shaped steel object comprises retained austenite, whichprovides beneficial properties as discussed further below. If quenchingwere to be performed to a temperature below Mf, the resulting shapedsteel object would be about 100% martensite. Therefore, the amount ofretained austenite in the shaped steel object is tunable. For example, ahighest retained austenite content is achieved by quenching to atemperature near, but below Ms 64 and a lowest retained austenitecontent is achieved by quenching to a temperature near, but above Mf 66.As used herein, a temperature “near” Ms 64 or Mf 66 is a temperaturewithin about 200° C. of Ms 64 or Mf 66. Therefore, the amount ofretained austenite in the shaped steel object can be tuned or adjustedby quenching to a particular temperature between Ms 64 and Mf 66.

The optional tempering treatment then comprises heating the shaped steelobject to a temperature a treatment temperature 70 of greater than orequal to about 150° C. to less than or equal to about 300° C. for a timeperiod of greater than or equal to about 1 minute to less than or equalto about 120 minutes, or greater than or equal to about 5 minutes toless than or equal to about 60 minutes, as described above. Cooling theshaped steel object back to a temperature between Ms 64 and Mf 66, suchas ambient temperature 68, completes the method. In some embodiments,the shaped steel object is painted and tempering treatment is performedsimultaneously with a paint baking process during, for example, vehiclemanufacture.

Shaped steel objects made by the above methods, also referred to hereinas “hot stamped alloy”, have a higher strength and a lower weightrelative to an equivalent shaped steel object formed from 22MnB5, alsoreferred to as “hot stamped 22MnB5”. The higher strength is a result ofthe microstructure of the hot stamped alloy, which comprises greaterthan or equal to about 80 wt. % to less than or equal to about 95 wt. %martensite and greater than or equal to about 5 wt. % to less than orequal to about 20 wt. % retained austenite. Put another way, themicrostructure of the hot stamped alloy has a martensite:retainedaustenite ratio of from about 4:1 to about 19:1. The tempering treatmentstabilizes the retained austenite.

FIG. 4 shows an electron backscatter diffraction (EBSD) image of themicrostructure of a hot stamped alloy made according to the currentmethod. The image shows that the hot stamped alloy comprises martensite78 and retained austenite 79. The scale bar is 5 μm.

The presence of retained austenite in the hot stamped alloy increasesthe UTS and ductility (elongation) relative to an equivalent hot stampedalloy of 22MnB5 steel due to transformation induced plasticity (TRIP).The TRIP is an effect in which retained martensite transforms intostructure phase martensite upon application of a load or stress. Anexample of the TRIP effect is provided in FIG. 5 . FIG. 5 shows a firstmicrostructure 80 having grains A-E and retained austenite representedby diamonds 82 located between the grains A-E. When a load or stress isapplied, as shown by the arrow, the first microstructure 80 transformsinto a second microstructure 84, wherein the retained austenite 82transforms into martensite represented by circles 86.

Due to the TRIP effect, the martensite:retained austenite ratioincreases when a load or stress is applied to the hot stamped alloy.Because hot stamped 22MnB5 steel comprises about 100% martensite, itdoes not undergo the TRIP effect upon the application of a load orstress. Accordingly, at least partially due to the TRIP effect, the hotstamped alloy of the current technology has an increased strengthrelative to an equivalent hot stamped alloy of 22MnB5. The hot stampedalloy of the current technology has a UTS of greater than about 1500MPa, greater than about 1600 MPA, or greater than about 1700 MPA, suchas a UTS of greater than about 1500 MPa to less than or equal to about2200 MPa, or greater than or equal to about 1800 MPa to less than orequal to about 2000 MPa. Also, the hot stamped alloy of the currenttechnology has a ductility (elongation) of greater than or equal toabout 7% to less than or equal to about 15%, or greater than or equal toabout 10% to less than or equal to about 13%. Relative to an equivalenthot stamped object comprising 22MnB5 steel, the hot stamped alloycomposition of the current technology has an increase in UTS of fromgreater than or equal to about 10% to less than or equal to about 35%,or greater than or equal to about 10% to less than or equal to about15%.

An example of the increased strength provided by the current alloycomposition relative to 22MnB5 steel is shown in FIG. 6 . In particular,FIG. 6 provides a graph 90 with a y-axis 92 corresponding to stress(MPa) and an x-axis 94 corresponding to strain (%). The hot stamped22MnB5 is represented by squares and hot stamped alloy composition ofthe current technology is represented by stars. As shown by the blockarrow, the strength and ductility (elongation) of the hot stamped alloycomposition of the current technology are higher than the strength andductility (elongation) of the hot stamped 22MnB5.

FIG. 7 provides another graph 100 having a y-axis 102 corresponding tostress (MPa) and an x-axis 104 corresponding to strain (%). First curves106 from an object hot stamped from 22MnB5 and second curves 108 from anobject hot stamped from the alloy composition according the currenttechnology are shown on the graph 100. The graph 100 shows that theobject hot stamped from the alloy composition according to the currenttechnology has a higher strength and ductility relative to the objecthot stamped from 22MnB5 steel.

The lower weight of the shaped steel object is in part due to theincreased UTS. Because the shaped steel object has an increased strengthrelative to an equivalent object hot stamped from 22MnB5, thinnermaterial can be used for a weight reduction of greater than or equal toabout 15% to less than or equal to about 20%.

The lower weight is also a result of a high Al concentration. Iron (Fe)has a density of about 7.86 g/cm³ and aluminum (Al) has a density ofabout 2.7 g/cm³. This difference accounts for a 1.3% density reductionper 1 wt. % Al included in the alloy composition. The high Alconcentration of the alloy composition also results in lattice dilation.By replacing a portion of the Fe content with Al, leading to anincreased amount of Al relative to 22MnB5, the lower density, but largerAl atoms occupy more lattice space than the heavier and denser Fe atoms.Therefore, a lattice will dilate when iron in the lattice is replaced byAl. An example of lattice dilation is provided in FIG. 8 , which shows alattice 110 comprising Fe atoms 112 shown as circles with solid borders.The lattice 110 is packed as if all the atoms are Fe. An aluminum atom114 is shown as a shaded circle with a dashed border superimposed on acentral Fe atom (not shown). When the central Fe atom is replaced by theAl atom 114, the spacing of the Fe atoms 112 in the lattice 110 isforced to dilate in order to accommodate the relatively larger Al atom114. The increased amount of space occupied by Al relative to Fe alsocauses a weight reduction. Through this double mechanism provided by Al,i.e., lower density and lattice dilation, a weight reduction of greaterthan or equal to about 4% to less than or equal to about 11% relative toan equivalent hot stamped 22MnB5 is achieved.

Between the reduction of material that can be used relative to 22MnB5due to its higher UTS and ductility (elongation) and the double effectprovided by Al, the hot stamped object has a total weight decrease ofgreater than or equal to about 18% to less than or equal to about 28%relative an equivalent object hot stamped from 22MnB5.

The current technology further provides a shaped steel object made bythe above method. The shaped steel object has a higher strength, ahigher ductility, and a lower weight relative to a second shaped objectthat was hot stamped from 22MnB5. The shaped steel object may be part ofan automobile or other vehicle as exemplified above.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. An alloy composition comprising: carbon (C) at aconcentration of greater than or equal to about 0.05 wt. % to less thanor equal to about 0.5 wt. % of the alloy composition, manganese (Mn) ata concentration of greater than or equal to about 4 wt. % to less thanor equal to about 12 wt. % of the alloy composition, aluminum (Al) at aconcentration of greater than or equal to about 2 wt. % to less than orequal to about 8 wt. % of the alloy composition, vanadium (V) at aconcentration of greater than 0 wt. % to less than or equal to about 0.4wt. % of the alloy composition, and a balance of the alloy compositionbeing iron (Fe).
 2. The alloy composition according to claim 1, whereinthe alloy composition comprises: zirconium (Zr) at a concentration ofgreater than 0 wt. % to less than or equal to about 0.5 wt. % of thealloy composition.
 3. The alloy composition according to claim 2,wherein the alloy composition comprises: nitrogen (N) at a concentrationof greater than 0 wt. % to less than or equal to about 0.01 wt. %. 4.The alloy composition according to claim 3, wherein the alloycomposition comprises ZrN.
 5. The alloy composition according to claim2, wherein the alloy composition comprises at least one of: nickel (Ni)at a concentration of greater than 0 wt. % to less than or equal toabout 5 wt. % of the alloy composition, molybdenum (Mo) at aconcentration of greater than 0 wt. % to less than or equal to about 0.5wt. % of the alloy composition, niobium (Nb) at a concentration ofgreater than 0 wt. % to less than or equal to about 0.2 wt. % of thealloy composition, copper (Cu) at a concentration of greater than 0 wt.% to less than or equal to about 3 wt. % of the alloy composition,titanium (Ti) at a concentration of greater than 0 wt. % to less than orequal to about 0.1 wt. % of the alloy composition, nitrogen (N) at aconcentration of greater than 0 wt. % to less than or equal to about0.01 wt. % of the alloy composition, and boron (B) at a concentration ofgreater than 0 wt. % to less than or equal to about 0.005 wt. % of thealloy composition.
 6. The alloy composition according to claim 1,wherein the Mn is at a concentration of greater than or equal to about 6wt. % to less than or equal to about 10 wt. %.
 7. The alloy compositionaccording to claim 1, wherein the Al is at a concentration of greaterthan or equal to 2 wt. % to less than or equal to about 5 wt. %.
 8. Thealloy composition according to claim 1, wherein the C is at aconcentration of greater than or equal to about 0.1 wt. % to less thanor equal to about 0.45 wt. %.
 9. The alloy composition according toclaim 1, wherein the alloy composition has a higher strength and lowerweight after press hardening relative to an equivalent 22MnB5 steelafter press hardening.
 10. The alloy composition according to claim 1,wherein after press hardening, the alloy composition comprises greaterthan or equal to about 80 wt. % to less than or equal to about 95 wt. %martensite and greater than or equal to about 5 wt. % to less than orequal to about 20 wt. % retained austenite.
 11. The alloy compositionaccording to claim 1, wherein after press hardening, the alloycomposition has a martensite:retained austenite ratio that increaseswhen a load is applied to the alloy composition.
 12. The alloycomposition according to claim 1, wherein the C is at a concentration ofabout 0.5 wt. % of the alloy composition and the Mn is at aconcentration of about 12 wt. %.
 13. The alloy composition according toclaim 12, wherein the alloy composition has a martensite start (Ms)temperature less than ambient temperature.
 14. The alloy compositionaccording to claim 1, wherein the C is at a concentration of about 0.05wt. % of the alloy composition and the Mn is at a concentration of about4 wt. %.
 15. The alloy composition according to claim 14, wherein thealloy composition has a martensite final (Mf) temperature greater thanambient temperature.
 16. The alloy composition according to claim 1,wherein the alloy composition has a critical transformation temperature(A_(c3)) of greater than or equal to about 880° C. to less than or equalto about 1000° C.
 17. An automobile part comprising the alloycomposition according to claim 1, wherein the automobile part is apillar, a bumper, a roof rail, a rocker rail, a tunnel, a beam, or areinforcement.
 18. A method of forming a shaped steel object, the methodcomprising: heating a blank to a temperature of greater than or equal toabout 900° C. to less than or equal to about 950° C. for a time periodof greater than or equal to about 1 minute to less than or equal toabout 60 minutes to generate a heated blank, the blank being composed ofan alloy composition comprising: carbon (C) at a concentration ofgreater than or equal to about 0.05 wt. % to less than or equal to about0.5 wt. % of the alloy composition, manganese (Mn) at a concentration ofgreater than or equal to about 4 wt. % to less than or equal to about 12wt. % of the alloy composition, aluminum (Al) at a concentration ofgreater than or equal to 2 wt. % to less than or equal to about 8 wt. %of the alloy composition, vanadium (V) at a concentration of greaterthan 0 wt. % to less than or equal to about 0.4 wt. % of the alloycomposition, zirconium (Zr) at a concentration of greater than 0 wt. %to less than or equal to about 0.5 wt. % of the alloy composition, and abalance of the alloy composition being iron (Fe); forming the heatedblank into a predetermined shape to generate a stamped object; quenchingthe stamped object by decreasing the temperature of the stamped objectto about ambient temperature to form a shaped steel object comprisingmartensite and retained austenite; and tempering the shaped steel objectby heating the shaped steel object to greater than or equal to about150° C. to less than or equal to about 300° C. for a time period ofgreater than or equal to about 1 minute to less than or equal to about120 minutes and then decreasing the temperature of the shaped steelobject to ambient temperature.
 19. The method according to claim 18,further comprising: transferring the heated blank to a press, whereinthe heated blank is formed into a predetermined shape defined by thepress to generate the stamped object.
 20. The method according to claim18, wherein the shaped steel object is an automobile part selected fromthe group consisting of a pillar, a bumper, a roof rail, a rocker rail,a tunnel, a beam, and a reinforcement.